Flip chip technology plays an important role in the packaging of semiconductor devices. A flip chip microelectronic assembly includes a direct electrical connection between face down electronic components and substrates, such as circuit boards, using solder bumps as the interconnects. The use of flip chip packaging has dramatically grown as a result of the advantages in size, performance and flexibility flip chips have over other packaging methods.
Recently, copper pillar technology has been developed. Instead of using solder bumps, electronic components are connected to substrates by means of a copper pillar. The copper pillar technology achieves finer pitches with minimum probability of bump bridging, reduces the capacitance load of the circuits and allows the electronic components to perform at higher frequencies.
However, stress may cause cracks along the interface of the copper pillar and the solder used to bond the electronic component. The cracks may cause serious reliability concerns due to high leakage currents. The stress may also lead to underfill cracking along the interface of the underfill and the copper pillar. The cracks may propagate to the underlying low dielectric constant (low-K) dielectric layers of the substrate.
Accordingly, there is a need for an improved structure and method to form conductive pillar for a semiconductor wafer with robust electrical performance.